Evaluation of the tensile strength of Korean yellow poplar lumber

Abstract

This study was conducted to confirm the feasibility of using yellow poplar, which is a fast-growing hardwood species in Korea, as a structural material. Lumber was produced, and the mechanical grading and the knot diameter ratio on the wide surface measurement were performed for each grade of lumber. It was confirmed that the majority mechanical grades of yellow poplar were E10, E11, and E12, and the size of knot in the surface increased as the mechanical grades decreased. A fitted distribution of tensile strength of the lumbers was the Weibull distribution. As a result of calculating the tensile allowable stress using the 5th percentile value calculated by the Weibull distribution and the non-parametric method according to the mechanical grade, all the experimental values were higher than the minimum allowable stresses presented in the Korean industrial standards. However, for the low grades, there was no significant difference from the standard values. This was thought to be due to the large size of knots in low-grade lumber. It was expected that the prospect of using yellow poplar structural member will be higher if additional research is conducted on the restriction of knot size according to the mechanical grade.

Allowable bending properties of machine-graded Korean yellow poplar lumber

“…Lim et al (2010) used softwood visual grading standards to classify yellow poplar lumber and confirmed the possibility of using yellow poplar lumber as a structural material. Kim et al (2024) confirmed the feasibility of the application of MSR for yellow poplar lumber grading and calculated design value according to grading through full-size tensile tests.…”

“…It was considered that the difference between the two studies occurred due to the diameter of the logs used to produce lumber, as listed in Table 1. The largest number of lumber pieces in this study was produced from logs with a diameter of 500 mm or more, while the largest number of lumber pieces in Kim et al (2024) was produced from logs with a diameter of more than 300 mm and less than 400 mm (Table 1). Øvrum et al (2009) reported that the proportion of lumber with high machine grade increased as the diameter of logs decreased for Norway spruce.…”

“…3. MSR grade distribution of yellow poplar lumber for bending test Kim et al (2024) reported that the major proportion of machine grades for yellow poplar lumber were E10, E11, and E12. Compared with the result in this study, the proportion of machine grades was different even though the lumbers in both studies were collected from the same harvested area.…”

“…For the 5 th percentile value, parametric and non-parametric methods were used. Kim et al (2024) reported that the most suitable distribution for the parametric method was the 2parameter Weibull distribution in tension test. Therefore, in this study, the Weibull distribution was also used as a parametric method as shown in Eq.…”

“…Brittle failure was mainly governed by bending tests of yellow poplar lumber. Therefore, it was considered that the allowable bending strength could be calculated by using the Weibull distribution for the parametric method, as in the previous study of the tensile properties of yellow poplar lumber Kim et al (2024). This is because Weibull's weakest link theory assumes that the probability of defects in a larger body increases and the likelihood of brittle failure at low stress is higher (Moses and Prion 2004).…”